Method and apparatus for magnetic explorations



June 3, 1952 H. JENSEN 2,598,698

METHOD AND APPARATUS FOR MAGNETIC EXPLORATIONS Filed July 2 1946 3Sheets-Sheet l .HOMER JENSEN June 3, 1952 H. JENSEN 2,598,698

METHOD AND APPARATUS FOR MAGNETIC EXPLORATIONS Filed July 2, 946 5Sheets-Sheet 2 grwwwbob HOMER JENSEN flue mm;

June 3, 1952 H. JENSEN 2,598,693

METHOD AND APPARATUS FOR MAGNETIC EXPLORATIONS Filed July 2. 1946 A sShets-Sheet s [III] l NAL CONTROL APPARATU 3 MAGNETOMUI:

can NG MECHANISM gwuwm HOMER JENSEN Patented June 3, 1952 METHOD ANDAPPARATUS. FOR MAGNETIC EXPLORATIONS Homer Jensen, Philadelphia, Pa.

Application July 2, 1946, Serial No. 680,908

(Granted under the act of March 3, 1883, as

amended April 30, 1928; 3'70 0; G. 757) 7 Claims.

This invention relates generally to methods and apparatus for conductingmagnetic explorations from an aircraft in flight and more par ticularlyto improvements in the method and apparatus of my copending applicationfor Method and Apparatus for Magnetic Exploration, Serial No. 680,905,filed July 2, 1946.

In the aforesaid application, a standard Navy magnetic airbornedetector, identified as AN ASQe-SA and referred to hereinafter as MAD,is adapted to provide a continuous record trace corresponde ingto spacechanges in the total value of the earths magnetic field as the aircraft.support therefor moves along a predetermine traverse.

Photographic apparatus including a continuous-strip type camera isemployed therewith for producing a continuous photographic record of theterrain disposed along the traverse simultaneously with the recordtrace, and apparatus operable at will is employed to cause-anidentifying serial number to appear on. the film, and simultaneouslytherewith, to produce an edgemark on the record tape or chartupon whichthe record trace appears, thereby to provide data from which acontinuous correlation between the trace and the ground positionscorresponding thereto may be produced.

Printing apparatus also is operative-lyassociated with the recorderproviding th record trace and is adapted to cause identifying numberscorresponding to those appearing on the record film and data relating tothe sensitivity of the MAD and the magnetic value of the basev line ofthe record tape to be printed thereon at will, this being doneparticularly after base and/or sensitivity changes have been made at thecontrol boX of the MAD, the dials of which are operatively connected tocertain of the print.- ing wheels comprising the printing apparatus.

In the use of this apparatus in conducting geophysical surveys,continuous records of space changes in the absolute or static value ofthe earth's magnetic field and of the terrain are producedsimultaneously as the aircraft moves along predetermined traversesat'eaoh of several altitudes, and at selected interval therealong therecord chart is edge-marked, and simultaneously therewith, a serialnumber corresponding thereto is superimposed on the photographic recordof the terrain. At other intervals along the traverse, the printingapparatus is actuated to print on the recording chart a serial numbercorresponding to that appearing on the photographic record and datarelating to the sensitivity of the MAD and the magnetic value of thebase line of the recording chart.

Thereafter, in plotting charts providing the true relation between thevariations in the magnetic field and the ground positions correspondingthereto, it is necessary first to determine the true distances betweenthe edge-marks on the record chart by determining the correspondingdistances between the corresponding serial numbers on the photographicrecord in terms of known distances appearing thereon, and thereafter toconvert the curvilinear coordinates to rectangular coordinates andcorrect for distance variations and discontinuities in the record trace,the discontinuities therein being due to changes in the settings of thecontrol box dials.

From the charts, thus prepared, it is possible to draw isomagneticcontours from which logical inferences and accurate quantitativedeductions as to the nature of the substrata can be established.

According to the arrangement of the present invention, theaforedescribed step in printing the data relating to the control boxsettings on the record tape or chart is obviated by causing this data tobe photographed by the continuous-strip camera and by causing the shadowof a galvanometer needle to so move in relation to the slit in thecontinuous-strip camera as to produce on the photographic record a tracewhich is the equivalent of that otherwise .produced by the aforesaidrecorder, the signals from the MAD,

corresponding to the space changes in the field detected thereby,beingcaused to drive the galvanometer.

These signals are also caused to drive a recorder, as in the copendingapplication, since it usually is desirable to provide a visualindication of variations in the field.

In the use of the apparatus of the present invention in conductinggeophysical surveys, therefore, it merely becomes necessary to convertthe curvilinear coordinates of the record shadow trace to rectangularcoordinates and correct for sponse for purposes of such detection in themanner more fully set forth in the copending application of Lynn H.Rumbaugh et al. for Magnetic Exploration Method and Apparatus, SerialNo. 676,050, filed June 11, 1946.

It is an object of the present invention, therefore, to provide a newand improved method and apparatus for conducting geophysical surveysfrom an aircraft in flight.

Another object is to provide a method of geophysical surveying from anaircraft in flight wherein all of the necessary data is provided on asingle photographic record of the terrain disposed along the traverse ofthe aircraft.

Another object is to produce a record trace corresponding to variationsin the ambient magnetic field of an airborne detector.

Another object is to provide a method and apparatus for producing on acontinuous photographic record of the terrain disposed along thetraverse of an airborne magnetometer detector, a continuous record tracecorresponding to variations in the ambient magnetic field detected bythe magnetometer.

Still other objects, features and advantages of the present inventionare those implied from or inherent in the novel combination andarrangement of parts wherein the aforedescribed method of the inventionis practiced, the foregoing being accomplished by the specific apparatusand in the specific manner hereinafter more fully to appear, referencebeing had to the accompanying drawings wherein:

Fig l is, a diagrammatic View of an aircraft and an aerodynamic bodytowed thereby and suitable for use with the apparatus of the presentinvention for conducting magnetic surveys according to the methodthereof;

Fig. 2 is a sectional view of the continuous-strip camera illustratingthe manner of mounting of the recording galvanometer associatedtherewith;

Fig. 3 is a sectional view taken along the line 3-3 of Fig. 2;

Fig. 4 is a plan view of a portion of the photographic record obtainedin the use of the apparatus of the present invention; and

Fig. 5 is a diagrammatic view of the complete apparatus according to thepreferred embodiment of the invention, this apparatus being supported inpart in the aircraft and in part in the aerodynamic body of Fig. 1.

Referring now to the drawings for a more complete understanding of theinvention, the MAD equipment shown diagrammatically in Fig. 5 comprisesa magnetometer detector and an orienting mechanism therefor, whichcomponents are contained within the aerodynamic body I0, Fig. 1. Thebody or bird I0 is of non-magnetic construction and is towed from theaircraft II at a distance therefrom by a cable I2 so as to avoid theeffects of the magnetic field of the aircraft. The aircraft I I,accordingly, may be of any suitable type providing the desired speed andcapacity regardless of the amount of steel which it may contain, theinstallation of the MAD and the photographic apparatus employedtherewith being largely a matter of establishing connections between thecomponents of the apparatus and adapting and mounting the same withinthe aircraft. The bird, however, must be connected so as to beaerodynamically stable in fiight, a suitof Gerhard O Haglund forAerodynamic Body,

4 Serial No. 671,841, filed May 21, 1946, now Patent No. 2,551,596.

Towin cable I2 is a strain-cored multi-conductor cable and serves toelectrically interconmeet the magnetometer detector and orientingmechanism with the signal control apparatus therefor carried within theaircraft II, whereby, a detecting element in the bird is adapted to bemaintained in alignment with the direction of the earths magnetic fieldunder control of the signal control apparatus.

The signal control apparatus also operates to produce electrical signalswhich correspond to space changes in the total value of the earthsmagnetic field sensed by the aforesaid detector element, and thesesignals are applied by way of a cable conductor I3, control box I4, andcable conductor I5 to a recording milliammeter I6 to drive the pen [1thereof with respect to its coacting chart I8 whereby a record trace I9is produced on the chart. Recorder I6 preferably is of the E-A type ofspring-drive recorder well known in the art.

The electrical signals produced by the signal control apparatus alsooperate a galvanometer 2| whereby the pointer 22 thereof indicates inrelation to the scale associated therewith, the corresponding movementsof the recording pen IT.

The control box I 4 also includes a sensitivity adjusting dial 23 bymeans of which the full scale deflection of the recorder pen I! fromedge to edge of the chart may be controlled, the dial being provided,for example, with sensitivities of 50, 100, 200, 500, 1000 and 5000gammas, and the pointer 24 being movable into positions opposite thenumbers- 1 to 6 provided on dial plate 25 and corresponding to theaforesaid sensitivities.

The control box further includes a plurality of dials 26, 2'! and 28 anda control switch 29 which control means for nulling out predeterminedportions of the total field at the detector element and thus determinethe magnetic vaule of the center or base line 20 of the recording chart.

Dials 26 and 21 each have nine positions indicated thereon which areadapted to be moved into alignment with the reference lines 30 and 3|respectively, 50 gammas being provided between positions on dial 26, asindicated at 32, and 500 gammas being provided between positions on dial27, as indicated at 33. Dial 28 has 10 positions indicated thereon whichare adapted to be moved into alignment with the reference line 34, 5000gammas being provided between these positions, as indicated at 35.Control switch 23 is employed to add 2500 gammas, as indicated at 36, tothe nulled out portion of the field, this being useful under certainconditions of adjustment of dials 26 and 21.

Thus, in a total field at the detector element of approximatel 56,750gammas, thenulling means may be arranged to null out permanently 30,000gammas in the field, dial 28 may be set in position 5 thereof to nullout 25,000 gammas, dial21 set in position 3 thereof to null out 1,500gammas, and dial 26 set in position 5 thereof to null out 250 gammaswhereby the recorder pen I! is caused to assume a position on the baseline 20 of chart I8. Thereafter, upon variation in the field at thedetection element, the pen is caused to move to the right or to the leftaccording to increases or decreases in the value of the field from saidbase value of 56,750 gammas. Occasionally it becomes necessary to adjustthe control box dials 23 and 26 through 28, and rarely control switch29, to keep the pen on scale on the chart,

and at such times a break indicated at 31 on the chart, Fig, 5, occursin the trace l9.

A suitable milliammeter 38 is employed to indicate a constant value ofdirect current supplied for nulling purposes, variable portions of thecurrent being supplied to the pickup coil of the aforesaid detectingelement according to the adjustments of dials 26 through 28 and controlswitch 29. It is essential that the D. C. source of nulling current bemaintained at a constant value in order that adjustments of the dialsproduce field changes corresponding accurately to the gamma incrementsindicated thereby. For this purpose, knobs 39 and 42 are provided, the

knobs controlling means for adjusting the current value.

A voltmeter ll also is employed to indicate the value of the voltagesupplied to the MAD, this voltage being derived from the power source ofthe aircraft. The switch 49 is employed for controlling certain circuitsduring the routine test of the apparatus.

A control button 43, adapted to close a switch 45, is employed toactuate a register counter 45 having the numbers thereon arranged flushwith the front panel of the control box, and simultaneously therewith toactuate other apparatus employed in the control circuit thereof, as willappear more fully hereinafter.

The aforedescribed MAD equipment and the Camera 5G is preferably of thecontinuous-stripv type such, for example, as the Sonne S-7 manufacturedby the Chicago Aerial Survey Company, whereby a continuous photographicrecord of the terrain may be produced thereby, such a camera beingcharacterized by having a very narrow slit or optical opening 41 whichmay be adjusted for width, thereby resulting in an angle of acceptancewhich is extremely narrow, as indicated at :8 in Fig. 1.

Slit 47 is formed within a plate 49 which is strengthened structurallyby a pair of square bars 51 secured thereto on opposite sides of theslit. Plate d9 is secured to the bottom of a casing 52 which, in turn,is secured to the main body portion of the camera as by screws 53. Thebottom of casing 52 is provided with an opening 54 adjacent the slit 4!and formed arcuately as at 55 to receive the film 56 on drum 5'! inclosely spaced relation to the slit.

A casing cover plate 58 having a housing portion 59 for the main lens SIof the camera is secured to casing Mas by a plurality of screws 62. Aconventional galvanometer 63 is secured to the inner side of cover plate58 as by screws 64 and includes an indicating pointer or needle 65 whichis formed into a crank-shape to provide a needle portion 66 which liesadjacent slit 4'! between brace members 51 whereby a needleportion equalapproximately to the width of the slit may be disposed within the pathof the light rays passing through the slit over the entire width of thefilm as the needle moves angularly between the limits indicated at67-68, in Fig. 3. Thus, the galvanometer needle portion casts a shadowon the film, the-shadow taking the form of a continuous trace 69, Fig.4, as the film moves past the slit and the needle moves angularly inresponse to variable signals supplied to the galvanometer. These signalsare the same as those supplied to recorder i5, and thus, trace G9 isindicative of the variations in the field indicated by trace IS on therecorder.

The continuous-strip camera is not satisfactory for use at requiredaltitudes unless provision is made for stabilizing the images of theterrain recorded on the film thereof, distortion of the images otherwiseresulting from yawing, pitching and rolling of the aircraft in flight. Asuitable image stabilizing device is indicated generally at H and isdisclosed in detail in my copending application for Image StabilizingApparatus and Method, Serial No. 662,164, filed April 15, 194:6. Suificeit to state herein that the stabilizing device comprises a pair ofrefleeting elements l2 and 13 which are adapted to be gyroscopicallycontrolled so as to cause various portions of the light path from theterrain to the camera lens 6| to have minimum angles of deviation fromeach other whereby rotation of the images on the film, and resultantdistortion thereof, is reduced to a minimum.

Camera se is provided with a shutter 14 which is adapted to be actuatedby a solenoid 15 thereby to superimpose on the image of the terrain onthe film of the camera, images of a serial number appearing on aconventional register counter 76 and of the numbers appearing on fourconventional number wheels 11 through 8i; which are supported on acommon axis of rotation in a housing BI and comprise a number indicatorgenerally designated 82 and wheels ll through as are operativelyconnected, as by flexible cables 83 through 86, to the control dials 23and 26 through 28 respectively, the operative connections, for example,including gear drives of the same ratios between the cables and thewheels and between the cables and the operating shafts individual to thedials. Thus, numbers corresponding to the positions of the dials arecaused to appear on the film, as indicated at til in Fig. 4, the numeral2 indicating the sensitivity setting of dial 23 and numerals 7, 8 and 6indicating the base settings of dials 28, 2! and 26. of the control box.The serial number appearing on counter 15 appears on the film as at 58in Fig. 4. The numerals appearing on the photographic record will bespaced thereon at a constant film distance A from the ground positionscorresponding thereto.

A reflecting element 69 is employed to bring the register counter E5 andnumber indicator 82 into the field of view of a lens 9| which isemployed to bring the images of the numbers onto the film. The number onthe wheels of the register counted Hi and indicator 82 preferably arearranged backwards thereon so as to appear frontwards on the film asindicated in Fig. 4.

Register counters 45 and it may be of any suitable type such, forexample, as Western Electric register counters, type 12F.

Solenoid i5 and counters 45 and 16 are arranged in a simple seriescircuit including a battery 92 and the aforementioned switch 44 in thecontrol box whereby these parts are simultaneously energized to actuateshutter '34 and advance the serial numbers upon depression of button 43on the control box. This circuit may be traced from switch 44, conductor93, solenoid 15, conductor 94, counter 18, conductor 95, battery 92,conductor 96, counter 45, and thence by way of conductor 91 to the otherside of switch 44.

In the use of the aforedescribed apparatus in conducting geophysicalsurveys, the aircraft H and its associated magnetometer apparatus areflown along predetermined survey lines or traverses. The record tracesl9 and 69 and the photographic record 56 of the terrain are producedcontinuously during the course of the traverses, and the control dials23 and 26 through 28 are adjusted, as necessary, to keep pen I! on scaleon the chart l8, or to provide the desired magnitude of the pendeflections, as the case may be.

From time to time, the operator depresses button 43 on the control boxto superimpose on the photographic record of the terrain, a serialnumber and the magnetic data relating to the sensitivity of themagnetometer apparatus, and the magnetic value of a reference line forthe trace appearing on the photographic record.

Each time this data is caused to appear on the photographic record,number counters 45 and 16 are advanced, the serial number to bephotographed next appearing visually on counter 45.

From time to time, particularly at the beginning and end of eachtraverse, the operator makes a note of the serial numbers appearing atthe control box and these numbers appearing on the photographic recordidentify the several traverses.

After the traverses in a predetermined area I have been completed andthe film used therefor developed, the true distances between the serialnumbers on the photographic record are determined from known distancesthereon such, for example, as the distance between the intersection ofroad 98 with river 99 and road intersection I0 I Thereafter record trace69 is translated into copy traces giving the true relation between thevariation in the earths magnetic field and the ground positionscorresponding thereto, and from the copy traces isomagnetic contours areprepared, all in a manner set forth in the copending application of LynnH. Rumbaugh et al. for Method and Apparatus for Conducting GeophysicalSurveys, Serial No. 682,518, filed July 10, 1946.

From the foregoing, it should now be apparent that a method andapparatus for conducting magnetic explorations has been provided whichis well adapted to fulfill the aforestated objects of the invention, andwhile the invention has been described in particularity with respect toa specific method and apparatus which gives satisfactory results, itwill be understood that various changes may be made by those skilled inthe art to which the invention most nearly appertains without departingfrom the spirit and scope of the invention as defined by the appendedclaims.

The invention herein described and claimed may be manufactured and usedby or for the Government of the United States of America forgovernmental purposes without payment of any royalties thereon ortherefor.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

l. A method of geophysical surveying which comprises the steps of flyingan aircraft and magnetometer apparatus associated therewith along apredetermined traverse, measuring the total magnetic field with saidmagnetometer, producing a continuous composite photographic record ofthe terrain beneath the plumb line of the aircraft and of a shadow tracecorresponding to space changes in the total value of the earths magneticfield detected by the magnetometer apparatus as the aircraft moves alongthe traverse, and at selected intervals along the traverse superimposingon the photographic record a serial number and a plurality of numbersindicative of the sensitivity of the magnetometer apparatus and themagnetic value of a reference line for said trace.

2. A method of geophysical surveying which comprises the steps of flyingan aircraft and magnetometer apparatus associated therewith along apredetermined traverse, measuring the total magnetic field With saidmagnetometer, producing a continuous photographic record of the terrainbeneath the plumb line of the aircraft by use of a continuous-stripcamera having a narrow slit, causing the needle of a galvanometer whichis actuated in accordance with space changes in the total value of theearths magnetic field detected by the magnetometer apparatus to traversesaid slit in a manner to produce on the photographic record a traceindicative of said changes in the field, and at selected intervals alongthe traverse of the aircraft superimposing on the photographic record aserial number and a plurality of numbers indicative of the sensitivityof the magnetometer apparatus and the magnetic value of a reference linefor said trace.

3. A method of geophysical surveying which comprises the steps of flyingan aircraft and magnetometer apparatus associated therewith along apredetermined traverse, measuring the total magnetic field with saidmagnetometer, producing a continuous record trace corresponding to spacechanges in the total value of the earths magnetic field detected by saidmagnetometer apparatus as the aircraft moves along the traverse,producing a continuous composite photographic record of the terrainbeneath the plumb line of the aircraft and of a shadow tracecorresponding to said record trace, indicating visually the serialnumber appearing on a first register counter, at selected intervalsalong the traverse superimposing on the said composite photographicrecord a photographic record of a serial number appearing on a secondregister counter and corresponding to the serial number appearing on thefirst counter and a plurality of numbers corresponding respectively toapparatus dial settings indicative of the sensitivity of themagnetometer apparatus and of the magnetic value of the base line of therecord chart upon which the record trace appears, and advancing thenumbers on said counters simultaneously as each number of saidphotographic record is superimposed on said composite photographicrecord.

4. In apparatus of the character disclosed for conducting magneticexplorations from an aircraft in flight, the combination of acontinuousstrip camera adapted to produce a continuous photographicrecord of the terrain beneath the plumb line of the aircraft and havinga narrow slit through which light rays from the terrain are admitted tothe camera film, a galvanometer having a needle adapted to traverse saidslit so as to produce a shadow trace on the film, and magnetometerapparatus for actuating the needle of said galvanometer in accordancewith variations in the ambient total field detected by the magnetometerapparatus.

5. In apparatus of the character disclosed for conducting magneticexplorations from an aircraft in flight, the combination of acontinuousstrip camera adapted to produce a continuous photographicrecord of the terrain beneath the plumb line of the aircraft and havinga narrow slit through which light rays from the terrain are admitted tothe camera film, means adapted to intercept said light rays andstabilize the image of the terrain on the film, a galvanometer having aneedle adapted to traverse said slit so as to produce a shadow trace onthe film, and magnetometer apparatus for actuating the needle of saidgalvanometer in accordance with variations in the ambient total fielddetected by the magnetometer apparatus.

6. In apparatus of the character disclosed for conducting magneticexplorations from an aircraft in flight, the combination of magnetometerapparatus including a detecting element adapted to be maintained inalignment with the earths magnetic field, and photographic means adaptedto produce a continuous photographic record of the terrain beneath theaircraft and to produce on the recorded image of the terrain acontinuous shadow trace corresponding to the variations in the earthstotal magnetic field detected by said element as the aircraft moves.along a predetermined traverse.

7. In apparatus of the character disclosed for conducting geophysicalsurveys from an aircraft in flight, magnetometer apparatus including arecorder for producing a record trace on a recording chart correspondingto space changes in the absolute or static value of the earths totalmagnetic field as the aircraft moves along a predetermined traverse andalso including a control box having dials for indicating and adjustingthe sensitivity of said magnetometer apparatus and the magnetic value ofthe base line of the recording chart, a number indicator having aplurality of number wheels operatively connected to said dialsrespectively and adapted to indicate numbers corresponding to thesettings of the dials, a continuous-strip camera adapted to produce acontinuous photographic record of the terrain beneath the plumb line ofthe aircraft and having a narrow slit through which 10 light rays fromthe terrain are admitted to the camera film, means adapted to interceptsaid light rays and stabilize the image of the terrain on the film,means associated with the camera and operable at will for superimposingon the film thereof images of the numbers appearing on said numberwheels, and a galvanometer adapted to be actuated by the same signalssupplied to said recorder and including a needle adapted to traversesaid slit whereby a shadow trace corresponding to the record trace isproduced on the film.

HUBER JENSEN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,331,978 Brock et al. Feb. 24,1920 1,585,484 Gasser May 18, 1926 1,658,537 Reinhold Feb. 7, 19281,912,485 Kothny June 6, 1933 2,167,630 Bazzoni et al Aug. 1, 19392,307,646 Sonne Jan. 3, 1943 2,338,991 Arnold Jan. 11, 1944 2,406,870Vacquier Sept. 3, 1946 2,424,772 Rieber July 29, 1947 2,428,034 Nicholset al Sept. 30, 1947 2,468,554 Hull Apr. 26, 1949 2,518,513 Wyckoff Aug.15, 1950 2,555,209 Vacquier May 29, 1951 FOREIGN PATENTS Number CountryDate 319,867 Great Britain Oct. 3, 1929 OTHER REFERENCES Heiland, A. I.M. E. Transactions, 1932, pages 213 214.

Heiland, Engineering and Mining Journal, December 1935, pages 609-610.

Logachev, Geophysics, April 1946, pages 135-147.

The Airborne Magnetometer, in Geophysics, July 1946, pages 321-334.

